1. Field of Invention
The present invention relates to an electrically driven electromechanical device, and relates more particularly to an electromechanical device and an electrical device with the electromechanical device.
2. Description of Related Art
Electromechanical devices are used in many different fields, including telecommunications, optics, acceleration sensors, and biotechnology, and can be used for switches, filters, and other devices particularly in wireless terminal devices. As wireless terminal devices and other data communication devices have come into widespread use, small wireless terminal devices that are compatible with different communication systems have become desirable. Because the number of passive devices such as switches that are used inside the terminal housing increases in such multimode terminal devices, reducing the size of the passive devices is desirable.
Radio frequency MEMS (RF-MEMS) switches manufactured using microelectromechanical systems (MEMS) technology are one potential solution to this problem. An RF-MEMS switch is a switch that moves a movable microelectrode to mechanically switch the signal transmission path. Its advantages include outstanding RF characteristics such as ultralow insertion loss, high isolation, and linearity. RF-MEMS switches can also be manufactured in processes that are compatible with semiconductor manufacturing processes, can therefore be easily incorporated in RF integrated circuit (RF-IC) devices, and are expected to contribute greatly to reducing communication unit size.
Conventional RF-MEMS switches are mechanical switches that have a membrane or beam-shaped actuator that is supported by a cantilevered beam clamp or a fixed-fixed beam clamp fixing the actuator at both ends, and switch the signal transmission path by causing the actuator to contact or separate from an electrode. The drive power source of the actuator is commonly electrostatic power, but magnetic and other actuation methods are also known.
A series RF-MEMS switch that is inserted in series to the signal transmission path is described next. A thin membrane approximately several hundred micrometers long is formed as a movable electrode on an extension of the signal line carrying the RF signal. The distal end of the movable electrode is open when the switch is off. When a drive electrode is disposed directly below the movable electrode and a DC voltage is applied, the movable electrode is pulled by electrostatic force and deflects to the drive electrode side, thus contacting the signal electrode that outputs the signal. The signal path between the movable electrode and the signal electrode thus shorts, and the RF signal flows through the movable electrode to the signal electrode and turns on. If a DC potential is not applied to the drive electrode, the movable electrode and signal electrode do not make contact, and the RF signal is interrupted and turns off.
See, for example, US Patent Application Publication No. 2004/0031670A1.
However, when a strong signal is input to the electromechanical device, a potential difference is produced between the movable electrode and the drive electrode, and a problem known as self-actuation in which the movable electrode is unintentionally driven automatically by the electrostatic force occurs. Self-actuation can cause such problems as structural failure due to operational errors or a strong drive force, or make it difficult for electrodes that have made contact to separate, and thus is a cause of reduced reliability in electromechanical devices.
A solution to this problem is taught in US Patent Application Publication No. 2004/0031670A1. More particularly, power is passed to ground by turning a solid state device disposed parallel to the electromechanical device on so that high power is not input to the electromechanical device. This construction requires a solid state component, thus increasing both size and cost as a result of the increased number of components.